Pollution Profile And Ozone Formation Potential Investigation Of Volatile Organic Compounds In Different Functional Areas Of Guangzhou City

In recent years,with the rapid development of the economy and the intensification of urbanization,the air pollution become increasingly serious in Guangdong,which is an economic province with huge population in Pearl River Delta（PRD）region of China.In the PRD region,ozone（O3）has becoming a main atmospheric pollutant,which not only has a serious impact on the atmospheric environment,but also poses serious harmful to the ecological environment and human beings’health.At the same time,it is reported that the atmospheric volatile organic compounds（VOCs）are the key participators in the formation of ozone.The VOCs emitted by different pollution sources have become the important influencing factors of the complex air pollution problem of urban agglomerations in PRD region.Therefore,the pollution profiles of ambient VOCs in Guangzhou,a representative city in PRD region,were measured using both offline analysis（pre-concentrator-gas chromatography-mass spectrometry（Pre-concentrator-GC/MS））and online monitoring（proton transfer reaction time-of-flight mass spectrometer（PTR-TOF-MS））methods.Three different functional areas,which were vehicle detection station（VSD）,roadside of city expressway（RCE）,and Higher Education Mega Center（HEMC）,were selected as research locations.Further,we clarified the contribution of VOCs emitted from different functional areas to the formation of O3 in Guangzhou.The main research contents and results of this thesis are as follows:First,VOCs released from different functional areas were collected using 2.7-L stainless steel canisters,which were pre-cleaned five times using high purity nitrogen（99.999%）and pre-evacuated before sampling.The VOCs samples were detected using Pre-concentrator-GC/MS with the USEPA TO-15 method.The measurement results demonstrated the total concentration of VOCs（TVOCs）with mean values of 55.0 ppb,44.9 ppb and 24.5 ppb at VSD,RCE and HEMC sites,respectively.At VSD site,the dominant group was aromatic hydrocarbons（accounting for 41.4%of the concentrations of TVOCs）,in which toluene accounts for the largest proportion（accounting for 17.6%of the concentrations of TVOCs）.In contrast,aliphatic hydrocarbons were the dominant group at RCE and HEMC sites（accounting for 50.2%and 47.4%of the concentrations of TVOCs,respectively）,in which n-hexane was the major compound（accounting for 18.4%and 21.6%of the concentrations of TVOCs at RCE and HEMC sites,respectively）.The average contribution of TVOCs detected by Pre-concentrator-GC/MS to O₃ formation potential was 380μg m^-3,290μg m^-3 and 340μg m^-3,respectively;indicating that VOCs emitted from VSD functional area may be the largest contribution to O3 formation in Guangzhou,followed by HEMC and RCE sites.Further,PTR-TOF-MS analysis technology was used to investigate the pollution profiles of VOCs in the above three different functional areas.Comparatively,the mean TVOC levels analyzed with PTR-TOF-MS were much higher at all studied sites（the concentrations of TVOCs were 220,170 and 160 ppb at VSD,RCE and HEMC sites,respectively）.The main reason for this is that a large quantity of oxygenated VOCs（OVOCs accounting for 72.0%,76.3%and 73.5%of the concentrations of TVOCs at VSD,RCE and HEMC sites,respectively）could be detectable with PTR-TOF-MS,instead of by pre-concentrator-GC/MS.Among OVOCs,methanol was found as the most abundant component at all three studied sites.The assessment of atmospheric photochemical activity showed that the average contributions to ozone formation potential（OFP）were 8.5×10²,7.3×10² and 8.2×10²μg m^-3 from VOCs monitored using PTR-TOF-MS at VSD,RCE and HEMC sites,respectively,and OVOCs were the dominant contributors for OFP.By comparing the two detection techniques,it was found that PTR-TOF-MS can more quickly and comprehensively monitor the pollution profiles of VOCs in different functional areas and achieve accurate prediction of O3 formation potential.Overall,we found that VOCs and O3 pollution are very serious in Guangzhou.In particular,OVOCs is the most important VOC components for total OFP.The results can provide scientific and effective air pollution control strategies for environmental workers and government managers,as well as provide scientific reference and decision-making basis for research to improve regional air quality.